Monoclonal antibodies will be obtained that are specific for adult gastrointestinal and related tissues. Using indirect immunofluorescence techniques, we will attempt to discern the specificity and resolving power of these antibodies in fresh, fixed, and sectioned material with regard to: (1) cell types in normal tissues, (2) applicability to detection of presumptive "metaplasias" and particular tumors in material from animal experiments as well as human material. Studies with immunofluorescence will be supplemented by histochemical methods (for mucins, alkaline phosphatase, leucine aminopeptidase, etc.) and by standard H and E preparations. These studies may help to elucidate the roles that metaplasias may play both in tumor progression and in other disease states, such as in gallstone formation and in gastric and duodenal peptic ulcers.